1. Field of the Invention
This invention relates generally to occupant restraints as used in motor vehicles. More specifically, the present invention relates to an energy absorbing apparatus for use in occupant restraint systems, such as seat belts and steering columns, that provides variable energy absorption.
2. Disclosure Information
Energy absorbing devices for controlling the deceleration of an object have been used in motor vehicles for some time. Generally, all of these devices operate in response to being subjected to an impact force exceeding a predetermined minimum value. The energy associated with this impact force is dissipated by controllably decelerating the impacting object. This deceleration occurs over a predetermined distance while a device absorbs the energy initially possessed by the impacting object.
One such system is disclosed in U.S. Pat. No. 4,027,905, which illustrates a seat belt system for a motor vehicle having an energy absorbing device anchoring the seat belt to a motor vehicle body structure. Responsive to an impact force in excess of a predetermined minimum, a planar steel strip is forcibly drawn through a plurality of pins causing the strip to plastically deform, thereby absorbing energy. As the strip is drawn through the pins, the impacting object decelerates within a predetermined maximum deceleration. To maintain the initial deceleration below the predetermined maximum requires the proper selection of the thickness, width and material properties of the strip. After the initial deceleration, however, due to momentum and friction effects the impacting object may decelerate at a rate considerably less than the predetermined deceleration maximum. This results in a considerable reduction in the energy absorbed for a given distance of travel than might otherwise be desired.
It would therefore be desirable to have a energy absorbing system capable of variable impact force dissipation properties.